POWER OUTPUT AND MUSCLE METABOLISM DURING AND FOLLOWING RECOVERY FROM10 AND 20 S OF MAXIMAL SPRINT EXERCISE IN HUMANS

On two separate days eight male subjects performed a 10- or 20-s cycle ergometer sprint (randomized order) followed, after 2 min of recovery , by a 30-s sprint. Muscle biopsies were obtained from the vastus late ralis at rest, immediately after the first sprint and after the 2 min of recovery on both occasions. The anaerobic ATP turnover during the i nitial 10 s of sprint 1 was 129 +/- 12 mmol kg dry weight(-1) and decr eased to 63 +/- 10 mmol kg dry weight(-1) between the 10th and 20th s of sprint 1. This was a result of a 300% decrease in the rate of phosp hocreatine breakdown and a 35% decrease in the glycolytic rate. Despit e this 51% reduction in anaerobic ATP turnover, the mean power between 10 and 20 s of sprint 1 was reduced by only 28%. During the same peri od, oxygen uptake increased from 1.30 +/- 0.15 to 2.40 +/- 0.23 L min( -1), which partially compensated for the decreased anaerobic metabolis m. Muscle pH decreased from 7.06 +/- 0.02 at rest to 6.94 +/- 0.02 aft er 10 s and 6.82 +/- 0.03 after 20 s of sprinting (for all changes P < 0.01). Muscle pH did not change following a 2-min recovery period aft er both the 10- and 20-s sprints, but phosphocreatine was resynthesize d to 86 +/- 3 and 76 +/- 3% of the resting value, respectively (n.s. 1 0- vs. 20-s sprint). Following 2 min of recovery after the 10-s sprint subjects were able to reproduce peak but not mean power. Restoration of both mean and peak power following the 20-s sprint was 88% of sprin t 1, and was lower compared with that after the 10-s sprint (P < 0.01) . Total work during the second 30-s sprint after the 10- and the 20-s sprint was 19.3 +/- 0.6 and 17.8 +/- 0.5 kJ, respectively (P < 0.01). As oxygen uptake was the same during the 30-s sprints (2.95 +/- 0.15 a nd 3.02 +/- 0.16 L min(-1)), and [Phosphocreatine] before the sprint w as similar, the lower work may be related to a reduced glycolytic ATP regeneration as a result of the higher muscle acidosis.